\begin{tikzpicture}[>=Stealth,
    every node/.style={fill=white, inner sep=1pt, outer sep=3pt},
]
% 各坐标点的相对位置
%          B -- C
%          |    |
%  A ---   E -- F -- D
    \pgfmathsetmacro{\factor}{0.5}
    \pgfmathsetmacro{\bc}{2.8 * \factor}
    \pgfmathsetmacro{\be}{4.2 * \factor}
    \pgfmathsetmacro{\cd}{7.5 * \factor}
    \pgfmathsetmacro{\ae}{\be * 2.5}
    \pgfmathsetmacro{\jiaoa}{atan(\be/\ae)}
    \pgfmathsetmacro{\jiaod}{asin(\be/\cd)}
    \pgfmathsetmacro{\df}{\be * cot(\jiaod)} % \cf = \be
    \pgfmathsetmacro{\r}{0.7}

    \coordinate (A) at (0, 0);
    \coordinate (B) at (\ae, \be);
    \coordinate (C) at (\ae + \bc, \be);
    \coordinate (E) at (\ae, 0);
    \coordinate (D) at (\ae + \bc + \df, 0); % \ef = \bc

    \draw (A) node [below] {$A$}
        -- (B) node [above left] {$B$} node [midway, above, rotate=\jiaoa] {$i = 1:2.5$}
        -- (C) node [above right] {$C$} node [midway, above] {$2.8$米}
        -- (D) node [below] {$D$} node [midway, above, rotate=-\jiaod] {$7.5$米}
        -- (E) node [below] {$E$}
        -- cycle;
    \draw [dashed] (B) -- (E) node [midway, below, rotate=90] {$4.2$米};
    \draw (B) to[chuizu={skipline=true}] (E);

    \draw (A) + (0:\r) arc (0:\jiaoa:\r) node [midway, right] {$\alpha$};
    \draw [double] (D) + (180:\r) arc (180:180-\jiaod:\r) node [midway, left] {$\beta$};
\end{tikzpicture}

